Devices for active overvoltage protection

ABSTRACT

A circuit protection device is provided. The circuit protection device includes an active energy absorber that is coupled between two power lines in an electrical power distribution system and is configured to selectively conduct fault current responsive to overvoltage conditions. The active energy absorber includes an overvoltage protection module that includes two thyristors that are connected in anti-parallel with one another and a varistor that is connected with the overvoltage protection module as a series circuit. The series circuit including the varistor and the overvoltage protection module is connected between the power lines.

FIELD OF THE INVENTION

The present invention relates to circuit protection devices and, moreparticularly, to overvoltage protection devices and methods.

BACKGROUND

Frequently, excessive voltage or current is applied across service linesthat deliver power to residences and commercial and institutionalfacilities. Such excess voltage or current spikes (transientovervoltages and surge currents) may result from lightning strikes, forexample. The above events may be of particular concern intelecommunications distribution centers, hospitals and other facilitieswhere equipment damage caused by overvoltages and/or current surges andresulting down time may be very costly.

Typically, sensitive electronic equipment may be protected againsttransient overvoltages and surge currents using Surge Protective Devices(SPDs). For example, brief reference is made to FIG. 1, which is asystem including conventional overvoltage and surge protection. Anovervoltage protection device 10 may be installed at a power input ofequipment to be protected 50, which is typically protected againstovercurrents when it fails. Typical failure mode of an SPD is a shortcircuit. The overcurrent protection typically employed is a combinationof an internal thermal disconnector to protect the device fromoverheating due to increased leakage currents and an external fuse toprotect the device from higher fault currents. Different SPDtechnologies may avoid the use of the internal thermal disconnectorbecause, in the event of failure, they change their operation mode to alow ohmic resistance. In this manner, the device can withstandsignificant short circuit currents. In this regard, there may be nooperational need for an internal thermal disconnector. Further to theabove, some embodiments that exhibit even higher short circuit withstandcapabilities may also be protected only by the main circuit breaker ofthe installation without the need for a dedicated branch fuse.

Brief reference is now made to FIG. 2, which is a block diagram of asystem including conventional surge protection. As illustrated, a threephase line may be connected to and supply electrical energy to one ormore transformers 66, which may in turn supply three phase electricalpower to a main circuit breaker 68. The three phase electrical power maybe provided to one or more distribution panels 62. As illustrated, thethree voltage lines of the three phase electrical power may designatedas L1, L2 and L3 and a neutral line may be designated as N. In someembodiments, the neutral line N may be conductively coupled to an earthground.

Some embodiments include surge protective devices (SPDs) 104. Asillustrated, each of the SPDs 104 may be connected between respectiveones of L1, L2 and L3, and neutral (N). The SPD 104 may protect otherequipment in the installation such as the distribution panel amongothers. In addition, the SPDs may be used to protect all equipment incase of prolonged overvoltages. However, such a condition may force theSPD to conduct a limited current for a prolonged period of time, whichmay result in the overheating of the SPD and possibly its failure(depending on the energy withstand capabilities the SPD can absorb andthe level and duration of the overvoltage condition). A typicaloperating voltage of an SPD 104 in the present example may be about 400V(for 690V L-L systems). In this regard, the SPDs 104 will each performas an insulator and thus not conduct current during normal operatingconditions. In some embodiments, the operating voltage of the SPD's 104is sufficiently higher than the normal line-to-neutral voltage to ensurethat the SPD 104 will continue to perform as an insulator even in casesin which the system voltage increases due to overvoltage conditions thatmight arise as a result of a loss of neutral or other power systemissues.

In the event of a surge current in, for example, L1, protection of powersystem load devices may necessitate providing a current path to groundfor the excess current of the surge current. The surge current maygenerate a transient overvoltage between L1 and N. Since the transientovervoltage significantly exceeds that operating voltage of SPD 104, theSPD 104 will become conductive, allowing the excess current to flow fromL1 through SPD 104 to the neutral N. Once the surge current has beenconducted to N, the overvoltage condition ends and the SPD 104 maybecome non-conducting again. However, in some cases, one or more SPD's104 may begin to allow a leakage current to be conducted even atvoltages that are lower that the operating voltage of the SPD's 104.Such conditions may occur in the case of an SPD deteriorating.

As provided above, devices for protecting equipment from excess voltageor current spikes (transient overvoltages and surge currents) mayinclude products such as energy absorbers that may be based on varistorsincluding, for example, metal oxide varistors (MOVs) and/or siliconcarbide varistors and may not have a safe end of life mode of operation.Additionally, such devices may not provide protection at a voltage levelclose to the operating voltage of the device. Further, surge protectivedevice designs may not protect at voltage levels close to the nominalsystem voltage and may not be designed to absorb as much energy asenergy absorbers. Combinations of varistors and thyristors may not havea safe failure mode and may not protect against surge currents andtransient overvoltages in the absence of an external SPD. Therefore,surge protection products that provide low voltage protection level andprotection against temporary overvoltages (TOVs) implemented in afail-safe design are desirable.

SUMMARY

Some embodiments of the present invention are directed to a circuitprotection device comprising an active energy absorber that is coupledbetween two of multiple phase lines and/or a neutral line in anelectrical power distribution system and that is configured toselectively conduct fault current responsive to overvoltage conditions.

In some embodiments, the active energy absorber comprises an overvoltageprotection module that comprises two thyristors that are connected inanti-parallel with one another and a metal oxide varistor (MOV) that isconnected with the overvoltage protection module as a series circuit.Some embodiments provide that the series circuit including the MOV andthe overvoltage protection module is connected between any two of thephase lines and/or the neutral line.

Some embodiments provide that the active energy absorber furtherincludes an inductor that is connected in series with the series circuitincluding the MOV and the overvoltage protection module. In someembodiments, the MOV includes multiple MOVs that are connected inparallel with one another.

Some embodiments include a surge protective device that is connectedbetween the any two phase lines and/or the neutral line and that isconfigured to protect equipment that is connected thereto during anovervoltage condition by conducting a limited amount of current thatcorresponds to the overvoltage condition.

Some embodiments include a trigger circuit that is connected to the anytwo phase lines and/or the neutral line and to the overvoltageprotection module and that is configured to provide control signals tothe overvoltage protection module responsive to detecting a temporaryovervoltage condition across the any two phase lines and/or the neutralline. In some embodiments, the trigger circuit includes a comparisoncircuit that is configured to receive a voltage level signal and avoltage reference signal and to output an overvoltage trigger signalresponsive to the voltage level signal exceeding the voltage referencesignal and a gate trigger circuit that is configured to generate a gatetrigger signal responsive to the overvoltage trigger signal that isreceived by the overvoltage protection module and that causes theovervoltage protection module to conduct current corresponding to thetemporary overvoltage condition.

Some embodiments provide that the trigger circuit further includes anoptical isolation circuit that is connected between the comparisoncircuit and the gate trigger circuit and that is configured to provideelectrical isolation between the comparison circuit and the gate triggercircuit.

Some embodiments include a surge protective device that is connectedbetween the any two phase lines and/or the neutral line.

In some embodiments, the active energy absorber further includes asnubber circuit that is connected in parallel with the overvoltageprotection module. The snubber circuit may include a resistor and acapacitor that are connected in series with one another.

In some embodiments, the active energy absorber includes a surgeprotective device that is connected between the any two phase linesand/or the neutral line, an overvoltage protection module that includestwo thyristors that are connected in anti-parallel with one another, avaristor that is connected with the overvoltage protection module as aseries circuit that is connected between any two of the phase linesand/or the neutral line, an inductor that is connected in between thevaristor and the surge protective device, and a trigger circuit that isconnected to the any two phase lines and/or the neutral line and to thetwo thyristors and that is configured to provide control signals to thetwo thyristors responsive to detecting an overvoltage condition acrossthe any two of the plurality of phase lines and the neutral line.

Some embodiments of the present invention are directed to methods ofproviding power circuit protection. Such methods may include sensing,using a trigger circuit, an overvoltage condition on a power line andswitching an overvoltage protection device into a conducting mode thatis configured to clamp the voltage to a voltage limit corresponding toan operating voltage of the power circuit.

Some embodiments include, after switching the overvoltage protectiondevice into the conducting mode, sensing that the overvoltage conditionon the power line is not present, and switching the overvoltageprotection device into a non-conducting mode.

In some embodiments, the power circuit is an alternating current (AC)power circuit and the sensing the overvoltage condition may correspondto a first portion of a voltage waveform. After switching theovervoltage protection into a non-conducting mode, the method mayfurther include sensing, using the trigger circuit, another overvoltagecondition corresponding to a second portion of the voltage waveform. Theovervoltage protection device may be switched into a conducting modethat is configured to clamp the voltage to a second portion voltagewaveform voltage limit.

In some embodiments, switching the overvoltage protection device duringthe first portion of the voltage waveform includes switching a firstthyristor and switching the overvoltage protection device during thesecond portion of the voltage waveform includes switching a secondthyristor that is connected in anti-parallel with the first thyristor.

Some embodiments of the present invention are directed to a circuitprotection device that includes a first thyristor, a first varistor, asecond thyristor, and a second varistor. The first thyristor includes afirst anode that is connected to a first power line, a first cathode anda first gate. The first varistor is connected to the first anode. Thesecond thyristor includes a second anode that is connected to a secondpower line, and a second cathode that is connected to the first cathodeand a second gate. The second varistor is connected to the second anodeand to the first varistor.

In some embodiments, the first varistor is connected to the firstcathode, and the second thyristor is connected to the second cathode.

Some embodiments may include a trigger circuit that is connected to thefirst and second power lines and to the first gate and the second gate,wherein the trigger circuit is configured to provide control signals tothe first thyristor and/or the second thyristor responsive to detectinga temporary overvoltage condition across the first and second powerlines.

In some embodiments, the device further includes an inductor that isconnected to either the first anode or the second anode.

In some embodiments, the first varistor includes a plurality of firstvaristors that are connected in parallel with one another, and thesecond varistor comprises a plurality of second varistors that areconnected in parallel with one another.

In some embodiments, the first and second power lines include any two ofa plurality of phase lines and a neutral line.

In some embodiments, the device further includes an inductor thatincludes a first is connected between a junction of the first and secondvaristors and a junction of the first cathode and the second cathode.

In some embodiments, the device further includes a trigger circuit thatis connected to the first and second power lines, to the first gate andthe second gate, and to the junction of the first cathode and the secondcathode, wherein the trigger circuit is configured to provide controlsignals to the first thyristor and/or the second thyristor responsive todetecting a temporary overvoltage condition across the first and secondpower lines.

In some embodiments, an active energy absorber module includes first andsecond electrical terminals, a module housing, first and secondthyristors, and a varistor. The first and second thyristors are enclosedwithin the module housing and are electrically connected between thefirst and second electrical terminals. The varistor is enclosed withinthe module housing and is electrically connected to at least one of thefirst and second thyristors between the first and second electricalterminals.

In some embodiments, the varistor is connected in electrical series witheach of the first and second thyristors.

In some embodiments, the first and second thyristors are connected inanti-parallel between the first and second electrical terminals.

In some embodiments, the active energy absorber module further includesa second varistor enclosed within the module housing, the firstthyristor includes a first anode and a first cathode, the secondthyristor includes a second anode and a second cathode, the firstvaristor is electrically connected to the first anode and the firstcathode, and the second varistor is electrically connected to the secondanode and the second cathode.

In some embodiments, the active energy absorber module further includesan inductor connected between a junction of the first and secondvaristors and a junction of the first cathode and the second cathode.

In some embodiments, the active energy absorber includes a plurality ofvaristors enclosed within the module housing and connected in electricalparallel with one another between the first and second electricalterminals.

In some embodiments, the active energy absorber includes a triggercircuit enclosed within the module housing and electrically connected toeach of the first and second thyristors.

In some embodiments, the active energy absorber includes a wire portdefined in the module housing, and at least one electrical wireextending through the wire port and electrically connecting the firstand second thyristors to a trigger circuit external to the modulehousing.

According to some embodiments, the active energy absorber includes aninductor coil enclosed within the module housing and connected in serieswith the first and second thyristors between the first and secondelectrical terminals.

In some embodiments, the inductor coil includes a spirally extendingcoil strip defining a spiral coil channel, and an electricallyinsulating casing including a separator wall portion that fills the coilchannel.

In some embodiments, the active energy absorber includes an electricallyconductive meltable member enclosed within the module housing. Themeltable member is responsive to heat in the active energy absorber tomelt and form an electrical short circuit path across the first andsecond electrical terminals.

According to some embodiments, the module housing includes first andsecond electrodes, and the varistor and the first and second thyristorsare axially stacked between the first and second electrodes.

In some embodiments, the first electrode includes a housing electrodeincluding an end wall and an integral sidewall collectively defining acavity, and the second electrode extends into the cavity.

In some embodiments, the varistor and the first and second thyristorsare disposed in the cavity.

In some embodiments, the housing electrode is unitarily formed of metal.

In some embodiments, the active energy absorber includes a biasingdevice applying an axially compressive load to the varistor and thefirst and second thyristors.

It is noted that aspects of the invention described with respect to oneembodiment, may be incorporated in a different embodiment although notspecifically described relative thereto. That is, all embodiments and/orfeatures of any embodiment can be combined in any way and/orcombination. These and other objects and/or aspects of the presentinvention are explained in detail in the specification set forth below.

BRIEF DRAWING DESCRIPTION

The accompanying figures are included to provide a further understandingof the present invention, and are incorporated in and constitute a partof this specification. The drawings illustrate some embodiments of thepresent invention and, together with the description, serve to explainprinciples of the present invention.

FIG. 1 is a block diagram of a system including conventional surgeprotection.

FIG. 2 is a block diagram of a system including conventional surgeprotection.

FIG. 3 is a schematic block diagram illustrating a device for activeovervoltage protection according to some embodiments of the presentinvention.

FIG. 4 is a schematic block diagram illustrating a device for activeovervoltage protection according to some embodiments of the presentinvention.

FIG. 5 is a schematic block diagram illustrating a device for activeovervoltage protection according to some embodiments of the presentinvention.

FIG. 6 is a schematic block diagram illustrating a device for activeovervoltage protection according to some embodiments of the presentinvention.

FIG. 7 is a schematic block diagram illustrating a trigger device thatmay be used in any of the devices described with reference to FIGS. 3-6according to some embodiments of the present invention.

FIG. 8 is a block diagram illustrating operations for providing activeovervoltage protection according to some embodiments of the presentinvention.

FIG. 9 is a graph of voltage versus time in an overvoltage conditionbased on the overvoltage protection of some embodiments of the presentinvention.

FIG. 10 is a top perspective view of a multi-phase active energyabsorber module according to some embodiments of the invention.

FIG. 11 is a fragmentary, top perspective view of the multi-phase activeenergy absorber module of FIG. 10.

FIG. 12 is a fragmentary, bottom perspective view of the multi-phaseactive energy absorber module of FIG. 10.

FIG. 13 is a fragmentary, cross-sectional view of the multi-phase activeenergy absorber module of FIG. 10 taken along the line 13-13 of FIG. 11.

FIG. 14 is a top perspective view of an active energy absorber systemaccording to some embodiments of the invention.

FIG. 15 is an exploded, top perspective view of an active energyabsorber module according to some embodiments of the invention andforming a part of the active energy absorber system of FIG. 14.

FIG. 16 is a cross-sectional view of the active energy absorber moduleof FIG. 15 taken along the line 16-16 of FIG. 14.

FIG. 17 is a cross-sectional view of an active energy absorber moduleaccording to further embodiments of the invention.

FIG. 18 is a top perspective view of a trigger module forming a part ofthe active energy absorber module of FIG. 17.

FIG. 19 is a cross-sectional view of an active energy absorber moduleaccording to further embodiments of the invention.

FIG. 20 is a top perspective view of an active energy absorber moduleaccording to further embodiments of the invention.

FIG. 21 is a cross-sectional view of the active energy absorber moduleof FIG. 20 taken along the line 21-21 of FIG. 20.

FIG. 22 is an exploded, top perspective view of a coil assembly forminga part of the active energy absorber module of FIG. 20.

FIG. 23 is a bottom perspective view of a casing forming a part of thecoil assembly of FIG. 22.

FIG. 24 is a cross-sectional view of an active energy absorber moduleaccording to further embodiments of the invention.

FIG. 25 is an exploded, top perspective view of an active componentsubassembly forming a part of the active energy absorber module of FIG.24.

FIG. 26 is a schematic block diagram illustrating a device for activeovervoltage protection according to some embodiments of the presentinvention.

FIG. 27 is a cross-sectional view of an active energy absorber accordingto further embodiments of the invention.

FIG. 28 is an exploded, perspective view of the active energy absorberof FIG. 27.

FIG. 29 is a cross-sectional view of an active energy absorber accordingto further embodiments of the invention.

FIG. 30 is a cross-sectional view of an active energy absorber accordingto some embodiments of the invention.

FIG. 31 is a schematic block diagram illustrating a device for activeovervoltage protection according to some embodiments of the invention.

FIG. 32 is a cross-sectional view of an active energy absorber accordingto some embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which illustrativeembodiments of the invention are shown. In the drawings, the relativesizes of regions or features may be exaggerated for clarity. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein; rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art.

It will be understood that when an element is referred to as being“coupled” or “connected” to another element, it can be directly coupledor connected to the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlycoupled” or “directly connected” to another element, there are nointervening elements present. Like numbers refer to like elementsthroughout.

In addition, spatially relative terms, such as “under”, “below”,“lower”, “over”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “under” or “beneath”other elements or features would then be oriented “over” the otherelements or features. Thus, the exemplary term “under” can encompassboth an orientation of over and under. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

Well-known functions or constructions may not be described in detail forbrevity and/or clarity.

As used herein the expression “and/or” includes any and all combinationsof one or more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

To date, types of circuits for providing protection against transientovervoltages, temporary overvoltages and surge/lightning current mayinclude varistors that may be directly connected directly between thepower lines. The difference between a standard varistor used for theprotection against transient overvoltages and surge currents and avaristor used for the protection against temporary overvoltages, may bethat the second type may be in a conducting mode for a long period oftime (in the range of 100 to 300 ms or even more) for a current that mayrange between a few Amperes and several thousand Amperes, while thefirst type may be in a conducting mode for a very limited period of time(in the range of few μs to up to 5 ms) for a current that may rangebetween a few hundred Amperes and over 100 kA.

Therefore, when the varistors are used for the protection againsttemporary overvoltages they may conduct a significant current from thepower source in an effort to clamp the overvoltage that is generated bythe power source. As such, they may be required to absorb significantamounts of energy for a long duration. Additionally, when such varistorsfail, the failure mode may be a low impedance (i.e., short circuit)failure mode at the end of the device life.

Reference is now made to FIG. 3, which is a schematic block diagramillustrating a device for active overvoltage protection according tosome embodiments of the present invention. An active energy absorber 100may be connected between power lines 70, 72 in an electricaldistribution system and/or component. The power lines 70, 72 may includepower lines and/or a neutral line in a single phase power system orphase lines and/or a neutral line in a multiple phase system (e.g.,three phase power system). Thus, the active energy absorber 100 may beconnected between two phase or power lines and/or between a phase orpower line and a neutral line. The active energy absorber 100 mayprovide protection against temporary overvoltages with high energyabsorption withstand capabilities and a safe end of life operation.

Some embodiments provide that an active energy absorber 100 mayselectively conduct fault current responsive to overvoltage conditions.For example, some embodiments provide that when the active energyabsorber 100 is in a conducting mode, that the overvoltage condition maybe clamped to a specific voltage by absorbing energy corresponding tothe overvoltage fault condition that exceeds the clamped voltage. Someembodiments are directed to providing protection for temporary powersystem sourced overvoltage conditions that may be sustained for longerperiods than transient and/or surge voltages. In use and operation, someembodiments provide that the temporary overvoltages may be clamped to avoltage that is about and/or less than about two times the systemoperating voltage. For example, in a 220 Volt system, embodiments mayset a threshold voltage at about 450 Volts.

In some embodiments, the active energy absorber 100 includes anovervoltage protection module 101 that includes two thyristors 102, 104that are connected in anti-parallel with one another. The thyristors102, 104 of the overvoltage protection module 101 may be connected inseries with a varistor 106. The series circuit including the varistor106 and the overvoltage protection module 101 may be connected betweenany two of the power lines and the neutral line 70, 72.

Some embodiments provide that the active energy absorber 100 includes atrigger circuit 110 that is connected to the power/neutral lines 70, 72and to the overvoltage protection module 101. The trigger circuit 110may be configured to provide control signals to the overvoltageprotection module 101 responsive to detecting a temporary overvoltagecondition across the power/neutral lines 70, 72. For example, responsiveto detecting a voltage across power lines 70 and 72 that exceeds athreshold voltage, the trigger circuit 110 may generate signals to oneor both of the thyristors 102, 104 to turn on (i.e., become a lowresistance current conducting path). Once the thyristor 102, 104 isturned on, the varistor 106 may absorb electrical energy to clamp thevoltage between the power lines 70, 72 to a clamping voltage that maycorrespond to the threshold voltage.

By way of example, for a 240V system, the peak voltage may be 336V. Theuse of a varistor 106 with a Maximum Continuous Operating Voltage (MCOV)of 250 VAC as close as possible to the nominal voltage may be used suchthat during normal conditions the MOV 106 will not conduct any current.Typically such an MOV may have a voltage protection level of around1000V. During a TOV event, when the voltage rises above a predeterminedthreshold (e.g., 600V), then the trigger circuit will trigger one of thethyristors 102, 104, according to the AC voltage polarity. Once each oneof the thyristors 102, 104 are turned on, the MOV 106 may startconducting heavily in an effort to clamp the voltage. During the TOVevent, when the voltage starts dropping close to the voltagecorresponding to normal operation, the MOV 106 may start becomingincreasingly resistive and may start reducing the current flow. The MOV106 may conduct a very small leakage current (e.g., about 1 mA) at 336V.Thus, when the voltage drops to values close to the operating systemvoltage, the current through the thyristors 102, 104 may be reduced tovery low values and thus may turn off, for example, thyristors willtypically be in a conduction mode only when there is a current flowthrough them above a certain level, such as, for example, around 200 mA.

However, there are power systems that may need protection at much lowervoltage levels, for example 700V instead of 1000V. In such cases, toreduce the protection level, varistors 106 with lower MCOV, i.e. thinnervaristor disks, may be used. For example, the varistor may have a MCOVof 150 VAC instead of 250 VAC.

In some embodiments, the fault current corresponding to an overvoltagecondition may exceed the energy absorption capacity of a single varistor106. In such cases, the capacity of a varistor 106 may be increased byusing multiple varistors 106 that are arranged in parallel with oneanother. Some embodiments provide that the multiple parallel varistors106 may be configured in a single device.

In addition, an inductance 120 may be provided in one of the lines 70,72 to protect thyristors 102, 104 against a substantially instantaneouschange in current (di/dt) in the case of surge events when thethyristors 102, 104 are self triggered during transient overvoltageevents or surge currents due to the dV/dt that the thyristors 102, 104will be exposed to. In some embodiments, this inductance 120 may also beconsidered as part of the power system (cable length, transformers etc.)Some embodiments provide that the inductance 120 may be added to theline 70, 72.

Some embodiments provide that the power distribution system/device is analternating current (AC) system/device. In such embodiments, theanti-parallel thyristors 102, 104 may be alternatively activated tocorrespond to different portions of the voltage waveform. For example,in the event of an overvoltage condition during the positive half of thevoltage waveform, the second thyristor 104 may be turned on to becomeconducting as long as the voltage in that half of the waveform remainsabove a voltage threshold. Once the voltage in that portion of the cycledrops below the threshold voltage, the varistor 106 may cease to conductbecause the voltage is sufficiently low and the thyristor 104 may beturned off. If the fault condition continues into the next portion ofthe voltage waveform, when the negative voltage goes beyond the voltagethreshold in the negative direction, the thyristor 102 may be turned onto become conducting as long as the voltage in that half of the waveformis greater than the voltage threshold in the negative direction.

Some embodiments provide that the active energy absorber 100 describedabove may protect against temporary overvoltages having a slow rise timeof the voltage. However, the active energy absorber 100 may not providesufficient protection during surge events and transient overvoltages. Inthis regard, the device for active overvoltage protection may furtherinclude a surge protective device (SPD) 130 that may connected to thepower lines 70, 72 in parallel with the active energy absorber 100. TheSPD 130 may be configured to protect equipment that is connected theretoduring an overvoltage condition by conducting a limited amount ofcurrent that corresponds to the surge or transient overvoltagecondition. Some embodiments provide that an SPD 130 may be used incircuits where there are threats of transient overvoltages and surgecurrents because during such events, there will be an overvoltage, aswell as a high rate of rise of voltage, applied on the thyristors 102,104 for a period of at least a few μs. This may result because theresponse time of the trigger circuit 110 that will trigger thethyristors 102, 104 and connect the varistor 106 to the power lines 70,72 to clamp the overvoltage may take longer than the few μs. As such,the overvoltage that may be applied for a few μs may damage thethrysistors 102, 104 if such overvoltage exceeds the maximum operatingvoltage of the thyristors 102, 104.

In some embodiments, the device for active overvoltage protectionincluding an active energy absorber 100 described herein may beimplemented a device using discrete components for each of the partscomposing the circuit, i.e. the coil, the thyristors and the one or morevaristors in parallel. Some embodiments provide that the device foractive overvoltage protection including an active energy absorberdescribed herein may be implemented as an energy absorber as describedabove.

Reference is now made to FIG. 4, which is a schematic block diagramillustrating a device for active overvoltage protection according tosome embodiments of the present invention. The device for activeovervoltage protection includes an SPD 230 and an active energy absorber200 that includes a varistor 206, trigger circuit 210, overvoltageprotection module 201 including thyristors 202, 204 that are similar tothe SPD 130 and active energy absorber 100 that includes a varistor 106,trigger circuit 110, overvoltage protection module 101 includingthyristors 102, 104 discussed above regarding FIG. 3. As such,discussion of these components will be omitted for brevity.

In contrast with FIG. 3, the device of FIG. 4 provides that the inductor208 is a component of the active energy absorber 200. For example, theinductance 208 may be connected in series with the series circuitincluding the varistor 206 and the anti-parallel thyristors 202, 204 ofthe overvoltage protection module 201.

Reference is now made to FIG. 5, which is a schematic block diagramillustrating a device for active overvoltage protection according tosome embodiments of the present invention. The device for activeovervoltage protection includes an SPD 330, inductance 320, and anactive energy absorber 300 that includes a varistor 306, trigger circuit310, overvoltage protection module 301 including thyristors 302, 304that are similar to the SPD 130, inductance 120, and active energyabsorber 100 that includes a varistor 106, trigger circuit 110,overvoltage protection module 101 including thyristors 102, 104discussed above regarding FIG. 3. As such, discussion of thesecomponents will be omitted for brevity.

In some embodiments, the active energy absorber 300 may include asnubber circuit 312 that is connected in parallel with the overvoltageprotection module 301. Some embodiments provide that the snubber circuit312 includes a resistor 316 and a capacitor 314 that are connected inseries with one another.

In some embodiments, the snubber circuit 312 used in parallel to thethyristors 302, 304 may reduce and/or eliminate self triggering of thethyristors 302, 304 during surge events and/or transient overvoltageevents. In such cases, the thyristors 302, 304 may only be triggered bythe trigger circuit 310 that is reacting to temporary overvoltage eventsonly. In some embodiments, the inductance 320 may be omitted as thethryistors 302, 304 may not be expected to conduct surge currents.

Reference is now made to FIG. 6, which is a schematic block diagramillustrating a device for active overvoltage protection according tosome embodiments of the present invention. An active energy absorber 400may be connected between power lines 70, 72 in an electricaldistribution system and/or component. The power lines 70, 72 may includepower lines and/or a neutral line in a single phase power system orphase lines and/or a neutral line in a multiple phase system (e.g.,three phase power system). Thus, the active energy absorber 400 may beconnected between two phase or power lines and/or between a phase orpower line and a neutral line.

Some embodiments provide that an active energy absorber 400 mayselectively conduct fault current responsive to overvoltage conditions.For example, some embodiments provide that when the active energyabsorber 400 is in a conducting mode, that the overvoltage condition maybe clamped to a specific voltage by absorbing energy corresponding tothe overvoltage fault condition that exceeds the clamped voltage. Someembodiments are directed to providing protection for temporary powersystem sourced overvoltage conditions that may be sustained for longerperiods than transient and/or surge voltages.

In some embodiments, the active energy absorber 400 includes a triggercircuit 410 that may be similar to trigger circuit 110 as discussedabove regarding FIG. 3. As such, additional description thereof will beomitted.

The active energy absorber 400 may include a first thyristor 404including a first anode that is connected to a first power line 70, afirst cathode and a first gate and a varistor 406 that is connected tothe anode and the cathode of the first thyristor 404. In this regard,the first thyristor 404 and the first varistor 406 may be connected inparallel with one another and each be connected to the first power line70. The active energy absorber 400 may include a second thyristor 402that includes a second anode that is connected to a second power line72, a second cathode that is connected to the cathode of the firstthyristor 404, and a second gate. A second varistor 408 is connected tothe anode and the cathode of the second thyristor 402. In this regard,the second thyristor 402 and the second varistor 408 may be connected inparallel with one another and each be connected to the second power line72.

In some embodiments, the electrical circuit of the active energyabsorber 400 may include the SPD functionality. As such, someembodiments provide that the active energy absorber 400 may be usedwithout an additional and/or external SPD.

Further, during surge events and transient overvoltages, the thyristors402, 404 may be self triggered due to their internal parasiticcapacitance between the gate and the anode and the gate and the cathode.According to convention, this parasitic capacitance may be made by themanufacturers to be as low as possible in order to avoid the selftriggering of the thyristors 402, 404 in surge events and transientovervoltage events. However, in the current application, the parasiticcapacitance may be higher, which may improve the ease of manufacture. Inthis regard, the device may demonstrate improved sensitivity totriggering during surge events and transient overvoltage events. Assuch, the voltage may not reach very high values before the thryistor402, 404 is triggered and the voltage is clamped at the protection levelof the varistor 406, 408. In this regard, the device may consistentlyclamp at the voltage level of a single varistor 406, 408, regardless ofwhether the event is a temporary overvoltage, a surge current or atransient overvoltage.

The active energy absorber 400 may not use a snubber circuit as thiscircuit may avoid a false trigger of the thyristor due to high dV/dtduring surge events or transient overvoltages. Instead, the ability ofthe thyristors 402, 404 to self trigger may clamp the voltage through asingle varistor.

Some embodiments provide that an inductance 420 may be optionally usedto reduce the di/dt through the thyristors 402, 404 when they conduct asurge current. Some embodiments provide that the power lines 70, 72themselves have significant inductance due to their length, the size ofthe cables and any transformer installed upstream to the device.However, adding inductance 420 between the power line 70 and the devicemay result in increasing the protection level (clamping voltage) thatthe equipment will experience during surge events and transientovervoltages. In this regard, if the inductance of the power system isnot enough, then an additional in-line module could be added to increasethe overall inductance of the power line. Some embodiments provide thatsince two varistors are used in the same device, the energy absorptioncan be shared between them during conduction.

Further, this device may provide stand-alone self-triggered operationthat can be connected in a power system between two lines and provideprotection against temporary overvoltage, transient overvoltage and/orsurge/lightning currents.

Reference is now made to FIG. 7, which is a schematic block diagramillustrating a trigger device that may be used in any of the devicesdescribed with reference to FIGS. 3-6 according to some embodiments ofthe present invention. The trigger device 510 may include a rectifier512 that is configured to receive AC line voltage from the power lines70, 72 and convert the AC line voltage to a DC output voltage that is avoltage level signal which corresponds to the AC line voltage. Acomparison circuit 514 may receive the voltage level signal and avoltage reference signal Vref. The output of the comparison circuit 514may be based on the comparison between the voltage level signal and thevoltage reference signal Vref. For example, if the voltage level signalis less than Vref, then the output of the comparison circuit 514 maycorrespond to normal operating voltage levels on the power lines 70, 72.In contrast, if the voltage level signal is greater than Vref, then theoutput of the comparison circuit may change states to indicate that anovervoltage condition exists.

The output of the comparison circuit 514 may be received by one or moresignal driver circuits 516 that may amplify, invert and/or stabilize theoutput state of the comparison circuit 514. In some embodiments, anoptical isolation circuit 518 that receives an input corresponding tothe output of the comparison circuit 514 may provide electricalisolation between the comparison circuit 514 and a gate trigger circuit520 that is configured to generate one or more gate trigger signals ifthe output corresponding to the comparison circuit indicates anovervoltage condition on the power lines 70, 72. The gate triggersignal(s) may be received by the overvoltage protection module and maycause the overvoltage protection module to conduct current correspondingto the temporary overvoltage condition. For example, gate triggersignals may be received at each of the two thyristors in the activeenergy absorber embodiments disclosed herein.

Reference is now made to FIG. 8, which is a block diagram illustratingoperations for providing active overvoltage protection according to someembodiments of the present invention. According to some methods,operations may include sensing, using a trigger circuit, an overvoltagecondition on a power line (block 810). The power line may be a phasepower line in a multiple phase power system and/or a single phase powerline. The overvoltage condition may be relative to another power lineand/or a neutral line. Some embodiments provide that the overvoltagecondition may be a temporary overvoltage system that may last for asignificant period of time, such as, for example, 100 ms to 300 ms ormore, in contrast with a surge or transient overvoltage event that mayhave a much shorter duration.

In response to detecting the overvoltage condition, operations mayinclude switching an overvoltage protection device into a conductingmode (block 820). When the overvoltage protection device is switchedinto a conducting mode, the voltage on the power line is clamped to avoltage limit that corresponds to an operating voltage of the powercircuit. For example, the voltage limit may be clamped to some multipleof the operating voltage of the power circuit. In some embodiments, themultiple may be in a range from 1.4 to 3.0 such that the voltage isclamped to a voltage that is 1.4 to 3.9 times the system operatingvoltage. In some embodiments, the multiple may be around 2 such that thevoltage is clamped to a voltage that is around 2 times the systemoperating voltage. Some embodiments provide that the overvoltageprotection device includes one or more thyristors that are in serieswith an SPD and that are switched into a conducting mode. In suchembodiments, the SPD may serve to clamp the voltage by absorbing theenergy corresponding to the fault current.

Once the overvoltage condition has passed, operations may includesensing that the overvoltage condition on the power line is not present(block 830). This can be done following the feature of the thyristor inwhich it is disconnected from the power line when the conducted currentdrops below a certain threshold, such as, for example, around 200 mA. Asthe voltage drops, at some point the voltage will reach a level belowwhich the MOV connected in series to the thyristor will only allow acurrent of less than about 200 mA to be conducted therethrough. This mayalso signify that the TOV condition is elapsed. In response to detectingthat the overvoltage condition is not present, the overvoltageprotection device may be switched into a non-conducting mode (block840).

In some embodiments, the power circuit is an alternating current (AC)power circuit and sensing the overvoltage condition may correspond to afirst portion of a voltage waveform and that, after switching theovervoltage protection into a non-conducting mode, the trigger circuitmay sense another overvoltage condition corresponding to a secondportion of the voltage waveform. In such embodiments, the overvoltageprotection device may switch into a conducting mode that is configuredto clamp the voltage to a second portion voltage waveform voltage limit.For example, some embodiments provide that switching the overvoltageprotection device during the first portion of the voltage waveform isperformed using a first thyristor and switching the overvoltageprotection device during the second portion of the voltage waveform isperformed using a second thyristor that is connected in anti-parallelwith the first thyristor.

FIG. 9 is a graph of voltage versus time in an overvoltage conditionbased on the overvoltage protection of some embodiments of the presentinvention. As illustrated, the overvoltage condition begins at time T1.Once the voltage level reaches a voltage threshold (V-threshold) at timeT2, the overvoltage protection turns on to become conducting and thevoltage is clamped to a clamp voltage (V-clamp). As the overvoltagecondition subsides, the voltage level reduces from the clamp voltageV-clamp to the operating voltage V-operating until the voltage reducesto a level below the clamp voltage. During that reduction in voltage,once the fault current reaches a given trigger fault current level, theovervoltage protection turns off and thus ceases to conduct current attime T3. For example, some embodiments provide that the overvoltageprotection turns off when the given trigger fault current reaches about220 mA, however, the given trigger fault current may be more or lessthan 220 mA.

With reference to FIGS. 10-13, a mechanical embodiment of the electricalcircuit 100 of FIG. 3 is shown therein. The illustrated embodiment is amulti-phase active energy absorber module 901 that is a three phaseimplementation and therefore includes three active energy absorbersubassemblies 900 each corresponding to one of the active energyabsorbers 100 of FIG. 3. That is, the active energy absorber 100 of eachphase is embodied in a respective subassembly 900. Each subassembly 900includes an MOV module 920 (corresponding to the MOV 106), twothyristors 910, 912 (corresponding to the thyristors 102, 104), atrigger circuit 930 (corresponding to the trigger circuit 110), and afuse 934 as discrete components. Each subassembly 900 is electricallyconnected to and mechanical mounted on an electrically conductiveneutral plate 903 and includes a respective line terminal 902. A neutralterminal 904 is also connected to the neutral plate 903. The triggercircuit 930 is provided on a PCB 932. The subassemblies 900 and theneutral plate 903 are contained in a module housing 906.

In some embodiments, each MOV module 920 may be constructed as disclosedin one or more of U.S. Pat. No. 6,038,119 to Atkins et al. and U.S. Pat.No. 6,430,020 to Atkins et al., the disclosures of which areincorporated herein by reference. In some embodiments and as shown inFIG. 13, each MOV module 920 includes a metal housing electrode 922, ametal piston electrode 924, and plurality of varistor wafers 926 stackedbetween a head 924A of the electrode 924 and an electrode end wall 922Aof the housing 922. The varistor wafers 926 are connected in electricalparallel between the inner faces of the head 924A and the end wall 922Aby electrically conductive interconnect members 928. The electrodes 922and 924 collectively form a chamber 921A within which the varistors 926are contained and encapsulated.

The electrical circuit of FIG. 4 may be implemented using discretecomponents for each of the circuit components, similar to the embodimentdescribed with reference to FIGS. 10-13. In this case, each subassembly900 is further provided with an inductor corresponding to the inductor208.

In other embodiments, the electrical circuit of FIG. 6 is implemented orpackaged as an active energy absorber module including a singleintegrated device wherein the varistors 106 and thyristors 102, 104 areencapsulated in a sturdy housing assembly. With reference to FIGS.14-16, an active energy absorber system 1001 according to embodiments ofthe invention is shown therein. The system 1001 includes a modularactive energy absorber unit or module 1000 according to embodiments ofthe invention and an external trigger circuit 1002. One system 1001 maybe used for each of the active energy absorbers 400 in FIG. 6. Thetrigger circuit 1002 may be any suitable device incorporating thetrigger circuit 410 of FIG. 6. The trigger circuit 1002 may be packagedin a protective housing.

The active energy absorber module unit 1000 has a lengthwise axis A-A(FIG. 16). The active energy absorber module 1000 includes a firstelectrode or housing 1022, a piston-shaped second electrode 1024, fourspring washers 1028E, a flat washer 1028D, an insulating ring member1028C, three O-rings 1030A-C, an end cap 1028A, a retention clip 1028B,a meltable member 1032, an insulator sleeve 1034, and a cable gland1036. The active energy absorber module unit further includes an activecomponent subassembly 1040 including three internal interconnect members1054, 1056, 1058, two varistor members 1042, 1044, two thyristors 1046,1048, two contact plates 1050, 1052, two gate connectors 1062D, and twosignal cables 1062A-B.

The components 1022, 1024, 1028A-C collectively form a housing assemblydefining a sealed, enclosed chamber 1026. The components 1022, 1024,1028A-E, 1032 and 1040 are disposed axially between the housing and theelectrode along the lengthwise axis A-A, in the enclosed chamber 1026.

The housing 1022 has an end electrode wall 1022A and an integralcylindrical sidewall 1022B extending from the electrode wall 1022A. Thesidewall 1022B and the electrode wall 1022A form a chamber or cavity1022C communicating with an opening 1022D. A threaded post 1022Eprojects axially outwardly from the electrode wall 1022A. A wireaperture or port 1022F extends through the side wall 1022B.

The electrode wall 1022A has an inwardly facing, substantially planarcontact surface 1022G. An annular clip slot 1022H is formed in the innersurface of the sidewall 1022B. According to some embodiments, thehousing 1022 is formed of aluminum. However, any suitable electricallyconductive metal may be used. According to some embodiments, the housing1022 is unitary and, in some embodiments, monolithic. The housing 1022as illustrated is cylindrically shaped, but may be shaped differently.

The inner electrode 1024 has a head 1024A disposed in the cavity 1022Cand an integral shaft 1022B that projects outwardly through the opening1022D.

The head 1024A has a substantially planar contact surface 1024C thatfaces the contact surface 1022G of the electrode wall 1022A. A pair ofintegral, annular, axially spaced apart flanges 1024D extend radiallyoutwardly from the shaft 1024B and define an annular, sidewardly openinggroove 1024E therebetween. A threaded bore 1024F is formed in the end ofthe shaft 1024B to receive a bolt for securing the electrode 1024 to abusbar, for example. An annular, sidewardly opening groove 1024G isdefined in the shaft 1024B.

According to some embodiments, the electrode 1024 is formed of aluminum.However, any suitable electrically conductive metal may be used.According to some embodiments, the electrode 1024 is unitary and, insome embodiments, monolithic.

The electrodes 1022, 1024, the insulating ring 1028C and the end cap1028A collectively define an enclosed chamber 1026 containing themeltable member 1032 and the active component subassembly 1040.

An annular gap is defined radially between the head 1024A and thenearest adjacent surface of the sidewall 1022B. According to someembodiments, the gap has a radial width in the range of from about 3 to10 mm.

The meltable member 1032 is annular and is mounted on the electrode 1024in the groove 1024E. The meltable member 1032 is spaced apart from thesidewall 1022B a distance sufficient to electrically isolate themeltable member 1032 from the sidewall 1022B.

The meltable member 1032 is formed of a heat-meltable, electricallyconductive material. According to some embodiments, the meltable member1032 is formed of metal. According to some embodiments, the meltablemember 1032 is formed of an electrically conductive metal alloy.According to some embodiments, the meltable member 1032 is formed of ametal alloy from the group consisting of aluminum alloy, zinc alloy,and/or tin alloy. However, any suitable electrically conductive metalmay be used.

According to some embodiments, the meltable member 1032 is selected suchthat its melting point is greater than a prescribed maximum standardoperating temperature. The maximum standard operating temperature may bethe greatest temperature expected in the meltable member 1032 duringnormal operation (including handling overvoltage surges within thedesigned for range of the system 1001) but not during operation which,if left unchecked, would result in thermal runaway. According to someembodiments, the meltable member 1032 is formed of a material having amelting point in the range of from about 80 to 160° C. and, according tosome embodiments, in the range of from about 130 to 150° C. According tosome embodiments, the melting point of the meltable member 1032 is atleast 20° C. less than the melting points of the housing 1022 and theelectrode 1024 and, according to some embodiments, at least 40° C. lessthan the melting points of those components.

According to some embodiments, the meltable member 1032 has anelectrical conductivity in the range of from about 0.5×10⁶ Siemens/meter(S/m) to 4×10⁷ S/m and, according to some embodiments, in the range offrom about 1×10⁶ S/m to 3×10⁶ S/m.

The two varistors 1042, 1044, the two thyristors 1046, 1048, the twocontact plates 1050, 1052, the insulator member 1060, and the threeinterconnect members 1054, 1056, 1058 are axially stacked in the chamber1026 between the electrode head 1024 and the electrode wall 1022 andform an active component subassembly 1040. The subassembly 1040corresponds to or forms the parts of the electrical circuit shown inFIG. 6 as follows: the varistor 1042 corresponds to the varistor 406,the varistor 1044 corresponds to the varistor 408, the thyristor 1046corresponds to the thyristor 402, the thyristor 1048 corresponds to thethyristor 404, and the trigger circuit 1002 corresponds to the triggercircuit 410. The interconnect members 1054, 1056 and the contact plates1050, 1052 electrically interconnect the varistors 1042, 1044,thyristors 1046, 1048, and trigger circuit 1002 in the mannerrepresented in FIG. 6.

Each varistor member 1042, 1044 has first and second opposed,substantially planar contact surfaces 1043. According to someembodiments, each varistor member 1042, 1044 is a varistor wafer (i.e.,is wafer- or disk-shaped). However, varistor members 1042, 1044 may beformed in other shapes. The thickness and the diameter of the varistorwafers 1042, 1044 will depend on the varistor characteristics desiredfor the particular application. In some embodiments, each varistor wafer1042, 1044 has a diameter to thickness ratio of at least 3. In someembodiments, the thickness of each varistor wafer 1042, 1044 is in therange of from about 1.5 to 15 mm.

The varistor wafers 1042, 1044 may include a wafer of varistor materialcoated on either side with a conductive coating so that the exposedsurfaces of the coatings serve as the contact surfaces. The coatings canbe formed of aluminum, copper or silver, for example.

The varistor material may be any suitable material conventionally usedfor varistors, namely, a material exhibiting a nonlinear resistancecharacteristic with applied voltage. Preferably, the resistance becomesvery low when a prescribed voltage is exceeded. The varistor materialmay be a doped metal oxide or silicon carbide, for example. Suitablemetal oxides include zinc oxide compounds.

The two thyristors 1046, 1048 may be constructed in the same or similarmanner. In some embodiments and as shown, the thyristors 1046, 1048 arewafer- or disk-shaped. In some embodiments, each thyristor 1046, 1048has a diameter to thickness ratio of at least 15. In some embodiments,the thickness of each thyristor 1046, 1048 is in the range of from about1.5 to 10 mm.

It will be appreciated that in FIG. 16 the internal structure andcomponents of the thyristors 1046, 1048 are not shown in detail. Eachthyristor 1046, 1048 includes a body 1045A and an anode 1045C and acathode 1045B on axially opposed sides of the body 1045A. The anode1045C and the cathode 1045B have substantially planar contact surfaces.Each thyristor 1046, 1048 further includes a gate or control terminal1045F (FIG. 15). The gate terminal 1045F is located in the center of thesame plate as the cathode 1045B and is surrounded by (but electricallyinsulated from) the cathode 1045B. An annular insulator 1045G is axiallyinterposed between the anode 1045C and the cathode 1045B andelectrically insulates the anode 1045C from the cathode 1045B.

Suitable thyristors for the thyristors 1046, 1048 may be constructed asdisclosed in, for example, U.S. Pat. No. 4,956,696 to Hoppe et al., thedisclosure of which is incorporated herein by reference.

With reference to FIG. 16, the cable gland 1036 is affixed in the wireport 1022F. The signal cables 1062A, 1062B extend through the wire port1022F and the cable gland 1036 and into the chamber 1026. The cablegland 1036 is secured in the wire port 1022F. The cable gland 1036serves to mechanically retain or secure the wires in the port 1022F(providing strain relief) and to fully seal, plug or close the bore inthe side wall 1022B (e.g., hermetically).

The signal cable 1062A includes a gate wire 1762GA electricallyterminated at the control terminal 1045F of the thyristor 1046. Thesignal cable 1062A also includes a reference wire electricallyterminated at the cathode 1045B of the thyristor 1046. The signal cable1062B includes a gate wire 1762GB electrically terminated at the controlterminal 1045F of the thyristor 1048. The signal cable 1062B alsoincludes a reference wire electrically terminated at the cathode 1045Bof the thyristor 1048.

The gate wires 1062GA, 1062GB of the cables 1062A, 1062B are terminatedand electrically and mechanically connected to the control terminals1045F of the thyristors 1046, 1048 by the gate connectors 1062D. Eachgate connector 1062D may include a spring 1062E that loads or biases thegate connector 1062D against the associated control terminal 1045F.

The reference wires of the cables 1062A, 1062B may be thin wires orfoils, for example, interposed between each cathode 1045B and theopposing face of the adjacent contact plate 1050, 1052. In someembodiments, the reference wire is connected (e.g., by soldering) to athin metal sheet (e.g., with a thickness in the range of from about 0.1mm to 1 mm; not shown for simplicity) that is positioned between thecathode 1045B and the contact plate 1050, or 1052. The triggering ofeach thyristor 1046, 1048 is done through the two wires (i.e., a gatewire and a reference wire) of the respective signal cable 1062A, 1062B.

In other embodiments, the reference wires of the cables 1062A and 1062Bmay be mechanically terminated and electrically connected (e.g., bysoldering) to the bridge portions 1057B of the interconnect members 1054and 1056, respectively, as described below with reference to FIG. 27,for example. In that case, the reference wire of the cable 1062A wouldbe electrically connected to its cathode 1045B through the interconnectmember 1054 and the contact plate 1050, and the reference wire of thecable 1062B would be connected to its cathode 1045B through theinterconnect member 1056 and the contact plate 1052.

The contact plates 1050, 1052 are electrically conductive. Each contactplate 1050, 1052 is disk-shaped and has opposed contact surfaces 1051A.Each contact plate 1050, 1052 also has formed therein a central throughhole 1051B and a slot 1051C extending radially from the through hole1051B to the outer periphery of the contact plate 1050, 1052. Eachcontrol or gate wire of the signal cables 1062A, 1062B is routed throughthe slot 1051C of a corresponding contact plate 1050, 1052 and eachassociated gate connector 1062D is seated in the through hole 1051B ofthe corresponding contact plate 1050, 1052.

According to some embodiments, the contact plates 1050, 1052 are formedof copper alloy. However, any suitable electrically conductive metal maybe used. According to some embodiments, the contact plates 1050, 1052are unitary and, in some embodiments, monolithic.

The interconnect members 1054, 1056, 1058 are electrically conductive.Each interconnect member 1054, 1056, 1058 includes a pair of axiallyspaced apart, disk-shaped contact portions 1057A joined by a bridgeportion 1057B.

According to some embodiments, the interconnect members 1054, 1056, 1058are formed of copper. However, any suitable electrically conductivemetal may be used. According to some embodiments, the interconnectmembers 1054, 1056, 1058 are unitary and, in some embodiments,monolithic.

The insulator member 1060 may be a relatively thin layer or disk of anelectrically insulating material. In some embodiments, the insulatormember 1060 has a thickness in the range of from about 1 to 10 mm.

According to some embodiments, the insulator member 1060 is formed of ahard, high temperature polymer and, in some embodiments, a hard, hightemperature thermoplastic. In some embodiments, the insulator member1060 is formed of mica.

According to some embodiments, the insulator member 1060 is formed of amaterial having a melting point greater than the melting point of themeltable member 1032. According to some embodiments, the insulatormember 1060 is formed of a material having a melting point in the rangeof from about 120 to 200° C.

According to some embodiments, the insulator member 1060 material canwithstand a voltage of 25 kV per mm of thickness.

According to some embodiments, the insulator member 1060 has a thicknessin the range of from about 0.1 to 10 mm.

The insulator sleeve 1034 is tubular and generally cylindrical.According to some embodiments, the insulator sleeve 1034 is formed of ahigh temperature polymer and, in some embodiments, a high temperaturethermoplastic. In some embodiments, the insulator sleeve 1034 is formedof polyetherimide (PEI), such as ULTEM™ thermoplastic available fromSABIC of Saudi Arabia. In some embodiments, the membrane 1060 is formedof non-reinforced polyetherimide.

According to some embodiments, the insulator sleeve 1034 is formed of amaterial having a melting point greater than the melting point of themeltable member 1032. According to some embodiments, the insulatorsleeve 1034 is formed of a material having a melting point in the rangeof from about 120 to 200° C.

According to some embodiments, the insulator sleeve 1034 material canwithstand a voltage of 25 kV per mm of thickness.

According to some embodiments, the insulator sleeve 1034 has a thicknessin the range of from about 0.1 to 2 mm.

The spring washers 1028E surround the shaft 1024B. Each spring washer1028E includes a hole that receives the shaft 1024B. The lowermostspring washer 1028E abuts the top face of the head 1024A. According tosome embodiments, the clearance between the spring washer hole and theshaft 1024B is in the range of from about 0.015 to 0.035 inch. Thespring washers 1028E may be formed of a resilient material. According tosome embodiments and as illustrated, the spring washers 1028E areBelleville washers formed of spring steel. While two spring washers1028E are shown, more or fewer may be used. The springs may be providedin a different stack arrangement such as in series, parallel, or seriesand parallel.

The flat metal washer 1028D is interposed between the uppermost springwasher 1028E and the insulator ring 1028C with the shaft 1024B extendingthrough a hole formed in the washer 1028D. The washer 1028D serves todistribute the mechanical load of the upper spring washer 1028E toprevent the spring washer 1028E from cutting into the insulator ring1028C.

The insulator ring 1028C overlies and abuts the washer 1028D. Theinsulator ring 1028C has a main body ring and a cylindrical upper flangeor collar extending upwardly from the main body ring. A hole receivesthe shaft 1024B. According to some embodiments, the clearance betweenthe hole and the shaft 1024B is in range of from about 0.025 to 0.065inch. An upwardly and outwardly opening peripheral groove is formed inthe top corner of the main body ring.

The insulator ring 1028C is preferably formed of a dielectric orelectrically insulating material having high melting and combustiontemperatures. The insulator ring 1028C may be formed of polycarbonate,ceramic or a high temperature polymer, for example.

The end cap 1028A overlies and abuts the insulator ring 1028C. The endcap 1028A has a hole that receives the shaft 1024B. According to someembodiments, the clearance between the hole and the shaft 1024B is inthe range of from about 0.1 to 0.2 inch. The end cap 1028A may be formedof aluminum, for example.

The clip 1028B is resilient and truncated ring shaped. The clip 1028B ispartly received in the slot 1022H and partly extends radially inwardlyfrom the inner wall of the housing 1022 to limit outward axialdisplacement of the end cap 1028A. The clip 1028B may be formed ofspring steel.

The O-ring 1030B is positioned in the groove 1024G so that it iscaptured between the shaft 1024B and the insulator ring 1028C. TheO-ring 1030A is positioned in the groove in the insulator ring 1028Csuch that it is captured between the insulating member 1028C and thesidewall 1022B. The O-ring 1030C is positioned in the groove 1024H toseal with the insulator ring 1028C. When installed, the O-rings 1030A-Care compressed so that they are biased against and form a seal betweenthe adjacent interfacing surfaces. In an overvoltage or failure event,byproducts such as hot gases and fragments from the thyristors 1046,1048 or varistors 1042, 1044 may fill or scatter into the cavity chamber1026. These byproducts may be constrained or prevented by the O-rings1030A-C from escaping the active energy absorber module 1000 through thehousing opening 1022D.

The O-rings 1030A-C may be formed of the same or different materials.According to some embodiments, the O-rings 1030A-C are formed of aresilient material, such as an elastomer. According to some embodiments,the O-rings 1030A-C are formed of rubber. The O-rings 1030A-C may beformed of a fluorocarbon rubber such as VITON™ available from DuPont.Other rubbers such as butyl rubber may also be used. According to someembodiments, the rubber has a durometer of between about 60 and 100Shore A.

The electrode head 1024A and the housing end wall 1022A are persistentlybiased or loaded against the active component subassembly 1040 along aload or clamping axis C-C (FIG. 16) in directions F to ensure firm anduniform engagement between the above-identified interfacing contactsurfaces. This aspect of the unit 1000 may be appreciated by consideringa method according to the present invention for assembling the unit1000, as described below. In some embodiments, the clamping axis C-C issubstantially coincident with the axis A-A (FIG. 16).

The signal cables 1062A-B are secured in the bore of the cable gland1036. The cable gland 1036 is secured in the wire port 1022F (e.g.,using adhesive). The cables 1062A-B are connected to the terminals1045F, 1045G.

The components 1042, 1044, 1046, 1048, 1050, 1052, 1054, 1056, 1058,1060 are assembled to form the active component subassembly 1040 (FIG.16). The subassembly 1040 is placed in the cavity 1022C such that thelower contact surface or portion 1051A of the interconnect member 1056engages the contact surface 1022G of the end wall 1022A.

The O-rings 1030A-C are installed in their respective grooves.

The head 1024A is inserted into the cavity 1022C such that the contactsurface 1024C engages the upper contact surface or portion 1051A of theinterconnect member 1054.

The spring washers 1028E are slid down the shaft 1024B. The washer1028D, the insulator ring 1028C, and the end cap 1028A are slid down theshaft 1024B and over the spring washers 1028E. A jig (not shown) orother suitable device is used to force the end cap 1028A down, in turndeflecting the spring washers 1028E. While the end cap 1028A is stillunder the load of the jig, the clip 1028B is compressed and insertedinto the slot 1022H. The clip 1028B is then released and allowed toreturn to its original diameter, whereupon it partly fills the slot andpartly extends radially inward into the cavity from the slot 1022H. Theclip 1028B and the slot 1022H thereby serve to maintain the load on theend cap 1028A to partially deflect the spring washers 1028E. The loadingof the end cap 1028A onto the insulator ring 1028C and from theinsulator ring onto the spring washers is in turn transferred to thehead 1024A. In this way, the subassembly 1040 is sandwiched (clamped)between the head 1024A and the electrode wall 1022A.

When the active energy absorber module 1000 is assembled, the housing1022, the electrode 1024, the insulating member 1028C, the end cap1028A, the clip 1028B, the O-rings 1030A-C and the cable gland 1036collectively form a unit housing or housing assembly 1021 containing thecomponents in the chamber 1026.

In the assembled active energy absorber module 1000, the large, planarcontact surfaces of the components 1022A, 1024A, 1042, 1044, 1046, 1048,1050, 1052, 1054 can ensure reliable and consistent electrical contactand connection between the components during an overvoltage or surgecurrent event. The head 1024A and the end wall 1022A are mechanicallyloaded against these components to ensure firm and uniform engagementbetween the mating contact surfaces.

Advantageously, the active energy absorber module 1000 integrates twovaristors 1042, 1044 in electrical parallel in the same modular device,so that energy can be shared between the varistors 1042, 1044 duringelectrical conduction.

The design of the active energy absorber module 1000 providescompressive loading of the thyristors 1046, 1048 in combination with thevaristor wafers 1042, 1044 in a single modular unit. The active energyabsorber module 1000 provides suitable electrical interconnectionsbetween the electrodes 1042, 1044, thyristors 1046, 1048, and varistorwafers 1042, 1044, while retaining a compact form factor and providingproper thermal dissipation of energy from the varistors 1042, 1044.

The construction of the active energy absorber module 1000 provides asafe failure mode for the device. During use, one or more of thevaristors 1042, 1044 and the thyristors 1046, 1048 may be damaged byoverheating and may generate arcing inside the housing assembly 1021.The housing assembly 1021 can contain the damage (e.g., debris, gasesand immediate heat) within the active energy absorber module 1000, sothat the active energy absorber module 1000 fails safely. In this way,the active energy absorber module 1000 can prevent or reduce any damageto adjacent equipment (e.g., switch gear equipment in the cabinet) andharm to personnel. In this manner, the active energy absorber module1000 can enhance the safety of equipment and personnel.

Additionally, the active energy absorber module 1000 provides afail-safe mechanism in response to end of life mode in one of more ofthe varistors 1042, 1044. In case of a failure of a varistor 1042, 1044,a fault current will be conducted between the corresponding line (e.g.,Line 1 of FIG. 6) and the neutral line. As is well known, a varistor hasan innate nominal clamping voltage VNOM (sometimes referred to as the“breakdown voltage” or simply the “varistor voltage”) at which thevaristor begins to conduct current. Below the VNOM, the varistor willnot pass current. Above the VNOM, the varistor will conduct a current(i.e., a leakage current or a surge current). The VNOM of a varistor istypically specified as the measured voltage across the varistor with aDC current of 1 mA.

As is well known, a varistor has three modes of operation. In a firstnormal mode (discussed above), up to a nominal voltage, the varistor ispractically an electrical insulator. In a second normal mode (alsodiscussed above), when the varistor is subjected to an overvoltage, thevaristor temporarily and reversibly becomes an electrical conductorduring the overvoltage condition and returns to the first modethereafter. In a third mode (the so-called end of life mode), thevaristor is effectively depleted and becomes a permanent, non-reversibleelectrical conductor.

The varistor also has an innate clamping voltage VC (sometimes referredto as simply the “clamping voltage”). The clamping voltage VC is definedas the maximum voltage measured across the varistor when a specifiedcurrent is applied to the varistor over time according to a standardprotocol.

In the absence of an overvoltage condition, the varistor wafer 1042,1044 provides high resistance such that no current flows through theactive energy absorber module 1000 as it appears electrically as an opencircuit. That is, ordinarily the varistor passes no current. In theevent of an overcurrent surge event (typically transient; e.g.,lightning strike) or an overvoltage condition or event (typically longerin duration than an overcurrent surge event) exceeding VNOM, theresistance of the varistor wafer decreases rapidly, allowing current toflow through the active energy absorber module 1000 and create a shuntpath for current flow to protect other components of an associatedelectrical system. Normally, the varistor recovers from these eventswithout significant overheating of the active energy absorber module1000.

Varistors have multiple failure modes. The failure modes include: 1) thevaristor fails as a short circuit; and 2) the varistor fails as a linearresistance. The failure of the varistor to a short circuit or to alinear resistance may be caused by the conduction of a single ormultiple surge currents of sufficient magnitude and duration or by asingle or multiple continuous overvoltage events that will drive asufficient current through the varistor.

A short circuit failure typically manifests as a localized pinhole orpuncture site (herein, “the failure site”) extending through thethickness of the varistor. This failure site creates a path for currentflow between the two electrodes of a low resistance, but high enough togenerate ohmic losses and cause overheating of the device even at lowfault currents. Sufficiently large fault current through the varistorcan melt the varistor in the region of the failure site and generate anelectric arc.

A varistor failure as a linear resistance will cause the conduction of alimited current through the varistor that will result in a buildup ofheat. This heat buildup may result in catastrophic thermal runaway andthe device temperature may exceed a prescribed maximum temperature. Forexample, the maximum allowable temperature for the exterior surfaces ofthe device may be set by code or standard to prevent combustion ofadjacent components. If the leakage current is not interrupted at acertain period of time, the overheating will result eventually in thefailure of the varistor to a short circuit as defined above.

In some cases, the current through the failed varistor could also belimited by the power system itself (e.g., ground resistance in thesystem or in photo-voltaic (PV) power source applications where thefault current depends on the power generation capability of the systemat the time of the failure) resulting in a progressive build up oftemperature, even if the varistor failure is a short circuit. There arecases where there is a limited leakage current flow through the varistordue to extended in time overvoltage conditions due to power systemfailures, for example. These conditions may lead to temperature build upin the device, such as when the varistor has failed as a linearresistance and could possibly lead to the failure of the varistor eitheras a linear resistance or as a short circuit as described above. Athyristor may also fail in a short circuit in a similar manner as thevaristor when the energy dissipated on the thyristor exceeds its powerdissipation limit, which may be represented by the current squared timesthe time (i²*t). The difference may be that under the same current levelconducted, the thyristor may dissipate far less energy so it is unlikelyto fail first, if the latter is properly designed and dimensional forspecific application. However, the manner of failure may be very similarto that of a MOV, namely through a low ohmic resistance path or apinhole that may generate an arc and/or overheating.

As discussed above, in some cases the active energy absorber module 1000may assume an “end of life” mode in which a varistor wafer 1042, 1044 isdepleted in full or in part (i.e., in an “end of life” state), leadingto an end of life failure. When the varistor reaches its end of life,the active energy absorber module 1000 will become substantially a shortcircuit with a very low but non-zero ohmic resistance. As a result, inan end of life condition, a fault current will continuously flow throughthe varistor even in the absence of an overvoltage condition. In thiscase, the meltable member 1032 can operate as a fail-safe mechanism thatby-passes the failed varistor and creates a permanent low-ohmic shortcircuit between the terminals of the active energy absorber module 1000in the manner described in U.S. Pat. No. 7,433,169, the disclosure ofwhich is incorporated herein by reference.

Each thyristor 1046, 1048 can likewise fail with the same or similarfailure modes as described herein for the varistors 1042, 1044,including failing as a short circuit, and failing as a linearresistance. The thyristors 1046, 1048 can likewise assume an “end oflife” mode as described for the varistors 1042, 1044. The thyristors1046, 1048 will exhibit similar or substantially the same behavior andresponse as described for the varistors 1042, 1044. As the failure modesof both the varistors and the thyristors are similar, the same by-passmechanism can be used inside the same chamber to enable the fail-safeoperation of the device 1000 when either a varistor 1042, 1044 or athyristor 1046, 1048 fails.

The meltable member 1032 is adapted and configured to operate as athermal disconnect to electrically short circuit the current applied tothe associated active energy absorber module 1000 around the varistors1042, 1044 and the thyristors 1046, 1048 to prevent or reduce thegeneration of heat in the varistors and thyristors. In this way, themeltable member 1032 can operate as switch to bypass the varistors 1042,1044 and thyristors 1046, 1048 and prevent overheating and catastrophicfailure as described above. As used herein, a fail-safe system is“triggered” upon occurrence of the conditions necessary to cause thefail-safe system to operate as described to short circuit the electrodes1022A, 1024A.

When heated to a threshold temperature, the meltable member 1032 willflow to bridge and electrically connect the electrodes 1022A, 1024A. Themeltable member 1032 thereby redirects the current applied to the activeenergy absorber module 1000 to bypass the varistors 1042, 1044 andthyristors 1046, 1048 so that the current induced heating of thevaristor or thyristor ceases. The meltable member 1032 may thereby serveto prevent or inhibit thermal runaway (caused by or generated in avaristor 1042, 1044 and/or a thyristor 1046, 1048) without requiringthat the current through the active energy absorber module 1000 beinterrupted.

More particularly, the meltable member 1032 initially has a firstconfiguration as shown in FIGS. 15 and 16 such that it does notelectrically couple the electrode 1024 and the housing 1022 exceptthrough the head 1024A. Upon the occurrence of a heat buildup event, theelectrode 1024 is thereby heated. The meltable member 1032 is alsoheated directly and/or by the electrode 1024. During normal operation,the temperature in the meltable member 1032 remains below its meltingpoint so that the meltable member 1032 remains in solid form. However,when the temperature of the meltable member 1032 exceeds its meltingpoint, the meltable member 1032 melts (in full or in part) and flows byforce of gravity into a second configuration different from the firstconfiguration. The meltable member 1032 bridges or short circuits theelectrode 1024 to the housing 1022 to bypass the varistors 1042, 1044and the thyristors 1046, 1048. That is, a new direct flow path or pathsare provided from the surface of the electrode 1024 to the surface ofthe housing sidewall 1022B through the meltable member 1032. Accordingto some embodiments, at least some of these flow paths do not includethe varistor wafers 1042, 1044 or the thyristors 1046, 1048.

According to some embodiments, the active energy absorber module 1000 isadapted such that when the meltable member 1032 is triggered to shortcircuit the active energy absorber module 1000, the conductivity of theactive energy absorber module 1000 is at least as great as theconductivity of the feed and exit cables connected to the device.

With reference to FIGS. 17 and 18, an active energy absorber module 1100according to alternative embodiments is shown therein. The active energyabsorber module 1100 corresponds to the active energy absorber module400 of the electrical circuit of FIG. 6. The active energy absorbermodule 1100 is constructed in the same manner as the active energyabsorber module 1000, except that the trigger circuit 1102 is integratedwithin the active energy absorber module 1100 and encapsulated in theenclosed chamber 1126 of the housing assembly 1121. As a result, theactive energy absorber module 1100 can operate as a stand-alone,self-triggering device that can be connected between two lines andprovide protection against overvoltage (temporary and transient) andsurge (e.g., lightning) events. Because the trigger circuit 1102 iscontained in the housing assembly 1121, the wire port 1022F can beeliminated.

In this case, with reference to FIG. 17, the inner electrode 1124 has atwo piece construction including a shaft member 1125 threadedly securedto a head member 1127. The trigger circuit 1102 is contained in atrigger circuit housing 1170A. The trigger circuit 1102 and the housing1170A together form a trigger circuit module 1170. The shaft member 1125extends through the housing 1170A and the trigger circuit module 1170 iscaptured between the head 1127 and an integral flange 1125A of the shaftmember 1125. A wire assembly 1162 corresponding to the wire assembly1062 electrically connects the trigger circuit 1102 to the thyristors.

With reference to FIG. 19, an active energy absorber module 1200according to alternative embodiments is shown therein. The active energyabsorber module 1200 is constructed in the same manner as the activeenergy absorber module 1100 (including a housing assembly 1221corresponding to the housing assembly 1021 and a trigger circuit module1270 and a trigger circuit 1202 encapsulated in the enclosed chamber1226), except that each of leg of the circuit includes three varistorwafers 1242 in parallel. This embodiment can provide higher energyabsorption than the active energy absorber module 1000 of FIG. 17, forexample (when the varistors are of the same construction as thevaristors).

With reference to FIGS. 20-23, an active energy absorber module 1300according to alternative embodiments is shown therein. The active energyabsorber module 1300 corresponds to the active energy absorber circuit400 of the electrical circuit of FIG. 6 except that the unit 1300further integrates the inductor 420 into the active energy absorbermodule 1300. The active energy absorber module 1300 is constructed inthe same manner as the active energy absorber module 1100 (including ahousing assembly 1321 corresponding to the housing assembly 1121, and atrigger circuit module 1370 and a trigger circuit 1302 encapsulated inthe chamber 1326), except that the active energy absorber module 1300further includes an integral inductance coil assembly 1380 encapsulatedin the cavity 1326. The coil assembly 1380 includes a coil 1381corresponding to the coil 420 of the electrical circuit of FIG. 6.

The coil assembly 1380 includes an electrically conductive outer coilmember 1382, an electrically conductive inner coil member 1384, anelectrically conductive interface plate 1385A, coupling fasteners 1385B,an electrically conductive terminal member or shaft 1386, an electricalinsulator sheet 1385C, an electrically conductive coupling member 1387,an electrically insulating casing 1388, and an electrically insulatingouter cover 1389. The coil members 1382, 1384 collectively form the coil1381.

The outer coil member 1382 includes a coil body 1382A, a spirallyextending coil strip 1382B defining a spiral coil channel 1382C, and acoupling extension 1382D. A threaded bore 1382E extends axially throughthe coil body 1382A. Similarly, the inner coil member 1384 includes acoil body 1384A, a spirally extending coil strip 1384B defining a spiralcoil channel 1384C, and a coupling extension 1384D. A threaded bore1384E extends axially through the coil body 1384A.

The interface plate 1385A is interposed between the coupling extensions1382D, 1384D and the three components are secured together by thefasteners 1385B. The insulator sheet 1385C is sandwiched between thecoil members 1382, 1384 to prevent or inhibit direct flow of electricalcurrent therebetween.

The casing 1388 includes an outer shell portion 1388A, an innerseparator wall portion 1388B, and an outer separator wall portion 1388C.The outer shell portion 1389 partially surrounds and encases thecomponents 1388A-C. The outer separator wall portion 1388C fills thecoil channel 1382C between the adjacent windings of the coil strip1382B. The inner separator wall portion 1388B fills the coil channel1384C between the adjacent windings of the coil strip 1384B. The cover1389 is fitted over the casing 1388.

The terminal shaft 1386 is mechanically secured and electricallyconnected in the bore 1382E and projects through a post hole 1388D inthe casing 1388, and above the casing 1388.

The coupling member 1387 is mechanically secured and electricallyconnected in the bore 1384E and projects through a post hole in thecover 1389. The coupling member 1387 is also mechanically andelectrically secured in a bore of the head 1327.

The components 1382, 1384, 1385A, 1386, 1387 are formed of metal and, insome embodiments, are formed of aluminum. According to some embodiments,each coil member 1382, 1384 is unitary and, in some embodiments,monolithic.

The casing 1388 may be formed of a dielectric or electrically insulatingmaterial having high melting and combustion temperatures. In someembodiments, the casing 1388 is formed of a polymeric material. In someembodiments, the casing 1388 includes an epoxy. In some embodiments, thecasing 1388 includes a material selected from the group consisting ofepoxy adhesive and/or epoxy cast resin or silicone elastomer. In someembodiments, the casing 1388 is monolithic. In some embodiments, thecasing 1388 includes a material selected from the group consisting ofepoxy adhesive and/or epoxy cast resin that is itself covered by anouter layer of a different material.

The outer casing layer 1389 may be formed of a different material thatthe casing 1388 in order to provide complementary properties. In someembodiments, the outer casing layer 1389 is formed of a material thatprovides enhanced moisture resistance as compared to the material of thecasing 1388. In some embodiments, the outer casing layer 1389 is formedof a silicone compound or PBT.

In use, current flows sequential through the terminal shaft 1386, theouter winding strip 1382B, the coupling extension 1382D, the interfaceplate 1385A, the coupling extension 1384D, the inner winding strip1384B, the coupling member 1387, and the head 1327.

By axially stacking the sequentially arranged coil strips 1382B, 1384B,the outer diameter of the active energy absorber module 1300 can bereduced.

Electrical protection devices according to embodiments of the presentinvention may provide a number of advantages in addition to thosementioned above. The devices may be formed so to have a relativelycompact form factor. The devices may be retrofittable for installationin place of similar type surge protective devices not having circuits asdescribed herein. In particular, the present devices may have the samelength dimension as such previous devices.

According to some embodiments, the areas of engagement between each ofthe electrode contact surfaces, the varistor contact surfaces, and thethyristor contact surfaces are each at least one square inch.

According to some embodiments, the biased electrodes (e.g., theelectrodes 1022 and 1024) apply a load to the varistors and thyristorsalong the axis C-C in the range of from 2000 lbf and 26000 lbf dependingon its surface area.

According to some embodiments, the combined thermal mass of the housing(e.g., the housing 1022) and the electrode (e.g., the electrode 1024) issubstantially greater than the thermal mass of each of the varistors andthe thyristors captured therebetween. As used herein, the term “thermalmass” means the product of the specific heat of the material ormaterials of the object multiplied by the mass or masses of the materialor materials of the object. That is, the thermal mass is the quantity ofenergy required to raise one gram of the material or materials of theobject by one degree centigrade times the mass or masses of the materialor materials in the object. According to some embodiments, the thermalmass of at least one of the electrode head and the electrode wall issubstantially greater than the thermal mass of the varistor orthyristor. According to some embodiments, the thermal mass of at leastone of the electrode head and the electrode wall is at least two timesthe thermal mass of the varistor or thyristor, and, according to someembodiments, at least ten times as great. According to some embodiments,the combined thermal masses of the head and the electrode wall aresubstantially greater than the thermal mass of the varistor orthyristor, according to some embodiments at least two times the thermalmass of the varistor or thyristor and, according to some embodiments, atleast ten times as great.

As discussed above, the spring washers 1028E are Belleville washers.Belleville washers may be used to apply relatively high loading withoutrequiring substantial axial space. However, other types of biasing meansmay be used in addition to or in place of the Belleville washer orwashers. Suitable alternative biasing means include one or more coilsprings, wave washers or spiral washers.

With reference to FIGS. 24 and 25, an active energy absorber system 1401including a trigger circuit 1402 and an active energy absorber module1400 according to alternative embodiments is shown therein. The activeenergy absorber module 1400 corresponds to the active energy absorber100 of the electrical circuit of FIG. 3 except that the trigger circuit110 is external to the unit 1400. The active energy absorber module 1400is constructed in the same manner as the active energy absorber module1000 (including a trigger circuit 1402 external to the housing assembly1421), except that the active component subassembly 1440 of the activeenergy absorber module 1400 is differently constructed than the activecomponent subassembly 1040 of the active energy absorber module 1000.

The active component subassembly 1440 includes one varistor wafer 1442,two thyristors 1446, 1448, two contact plates 1450, 1452, an insulatormember (layer or plate) 1460, and two interconnect members 1454, 1456axially stacked in the chamber 1421 between the electrode head 1424A andthe electrode wall 1422A. The varistor 1442 corresponds to the varistor106, the thyristor 1446 corresponds to the thyristor 102, the thyristor1448 corresponds to the thyristor 104, and the trigger circuit 1402corresponds to the trigger circuit 110. The trigger circuit 1402 isconnected to the active component subassembly 1440 by a wire assembly1462. The interconnect members 1454, 1456, the contact plates 1450,1452, electrically interconnect the varistor 1442, thyristors 1446,1448, and trigger circuit 1402 in the manner represented in FIG. 3. Asdiscussed above, the thyristors 1446, 1448 are relatively arranged in anelectrically antiparallel configuration.

Reference is now made to FIG. 26, which is a schematic block diagramillustrating a device for active overvoltage protection according tosome embodiments of the present invention. An active energy absorber1600 may be connected between power lines 70, 72 in an electricaldistribution system and/or component. The power lines 70, 72 may includepower lines and/or a neutral line in a single phase power system orphase lines and/or a neutral line in a multiple phase system (e.g.,three phase power system). Thus, the active energy absorber 1600 may beconnected between two phase or power lines and/or between a phase orpower line and a neutral line.

Some embodiments provide that an active energy absorber 1600 mayselectively conduct fault current responsive to overvoltage conditions.For example, some embodiments provide that when the active energyabsorber 1600 is in a conducting mode, that the overvoltage conditionmay be clamped to a specific voltage by absorbing energy correspondingto the overvoltage fault condition that exceeds the clamped voltage.Some embodiments are directed to providing protection for temporarypower system sourced overvoltage conditions that may be sustained forlonger periods than transient and/or surge voltages.

In some embodiments, the active energy absorber 1600 includes a triggercircuit 1610 that may be similar to trigger circuit 110 as discussedabove regarding FIG. 3. As such, additional description thereof will beomitted.

The active energy absorber 1600 may include a first thyristor 1604including a first anode that is connected to a first power line 70, afirst cathode and a first gate. The active energy absorber 1600 mayinclude a second thyristor 1602 that includes a second anode that isconnected to a second power line 72, a second cathode that is connectedto the cathode of the first thyristor 1604, and a second gate. In thisregard, the first thyristor 1604 and the second thyristor 1602 areconnected in series with one another in opposing directions relative toone another.

The active energy absorber 1600 may include a first varistor 1606 thatis connected to the anode of the first thyristor 1604 and a secondvaristor 1608 that is connected to the anode of the second thyristor1602 and to the first varistor 1606. In this regard, the first varistor1606 and the second varistor 1608 may be connected in series with oneanother. In this regard, the anode of first thyristor 1604 and the firstvaristor 1606 may each be connected to the first power line 70 and theanode of second thyristor 1602 and the second varistor 1608 may each beconnected to the second power line 72.

Some embodiments provide that a first inductance 1620 may be optionallyused to reduce the di/dt through the thyristors 1602, 1604 when theyconduct a surge current. Some embodiments provide that the power lines70, 72 themselves have significant inductance due to their length, thesize of the cables and any transformer installed upstream to the device.However, adding inductance 1620 between the power line 70 and the devicemay result in increasing the protection level (clamping voltage) thatthe equipment will experience during surge events and transientovervoltages. In this regard, if the inductance of the power system isnot enough, then an additional in-line module could be added to increasethe overall inductance of the power line. Some embodiments provide thatsince two varistors are used in the same device, the energy absorptioncan be shared between them during conduction.

In some embodiments, the active energy absorber 1600 includes a secondinductance 1622 that may be connected between the cathodes of the firstand second thyristors 1604, 1602 and the common terminal of the firstand second varistors 1606, 1608. The second inductance 1622 may protectthe first and second thyristors 1604, 1602 from experiencing anexcessive rate of change of current (e.g., di/dt). For example, in thecase of a surge event from line 1 70 to line 2 72, the voltage acrossthe first varistor 1606 may rise very fast, for example, exceeding thedV/dt of the first thyristor 1604. Then, after a certain period of timethe first thyristor 1604 may be self triggered. As this might not occurinstantly (depending on the internal construction of the first andsecond thryistors 1604, 1602 and the internal parasitic capacitancebetween anode and gate), if a delay occurs, then the surge currentthrough the first varistor 1606 may reach a specific value at the timethe first thyristor 1604 is self triggered. The second inductance 1622may prevent an instantaneous rise in the current through the firstthyristor 1604 and thus prevent exceeding the rate of change of currenttherethrough. Some embodiments provide that a small inductance value forthe second inductance 1622 may be sufficient to slow down this surgecurrent transition and protect the first thyristor 1604 from damage. Insome embodiments, a value of the second inductance 1622 may be in therange of 1 μH to 10 μH, however, such range is not limiting.

In some embodiments, the electrical circuit of the active energyabsorber 1600 may include the SPD functionality. As such, someembodiments provide that the active energy absorber 1600 may be usedwithout an additional and/or external SPD.

Further, during surge events and transient overvoltages, the thyristors1602, 1604 may be self triggered due to their internal parasiticcapacitance between the gate and the anode and the gate and the cathode.According to convention, this parasitic capacitance may be made by themanufacturers to be as low as possible in order to avoid the selftriggering of the thyristors 1602, 1604 in surge events and transientovervoltage events. However, in the current application, the parasiticcapacitance may be higher, which may improve the ease of manufacture. Inthis regard, the device may demonstrate improved sensitivity totriggering during surge events and transient overvoltage events. Assuch, the voltage may not reach very high values before the thyristor1602, 1604 is triggered and the voltage is clamped at the protectionlevel of the varistor 1606, 1608. In this regard, the device mayconsistently clamp at the voltage level of a single varistor 1606, 1608,regardless of whether the event is a temporary overvoltage, a surgecurrent or a transient overvoltage.

The active energy absorber 1600 may not use a snubber circuit as thiscircuit may avoid a false trigger of the thyristor due to high dV/dtduring surge events or transient overvoltages. Instead, the ability ofthe thyristors 1602, 1604 to self trigger may clamp the voltage througha single varistor.

Further, this device may provide stand-alone self-triggered operationthat can be connected in a power system between two lines and provideprotection against temporary overvoltage, transient overvoltage and/orsurge/lightning currents.

With reference to FIGS. 27 and 28, an active energy absorber module 1700according to alternative embodiments is shown therein. The active energyabsorber module 1700 corresponds to the active energy absorber module1600 of the electrical circuit of FIG. 26. The active energy absorbermodule 1700 is constructed in the same manner as the active energyabsorber module 1100 (FIG. 17), except as discussed below.

The module 1700 includes a trigger circuit module 1770 corresponding tothe trigger circuit module 1170 (FIG. 17) and including a triggercircuit corresponding to the trigger circuit 1610 (FIG. 26).

The module 1700 includes an active component subassembly 1740 disposedin the enclosed chamber 1726 between the housing electrode end wall1722A and the electrode head 1727. The active component subassembly 1740includes two varistors 1742, 1744, two thyristors 1746, 1748, twocontact plates 1750, 1752, an insulator 1760, and three interconnectmembers 1754, 1756, 1758, corresponding to components 1042, 1044, 1046,1048, 1050, 1052, 1060, 1054, 1056 and 1058 of the module 1000. Thecomponents of the subassembly 1740 correspond to or form parts of theelectrical circuit of FIG. 26 as follows: the varistor 1742 correspondsto the varistor 1606; the varistor 1744 corresponds to the varistor1608; the thyristor 1746 corresponds to the thyristor 1602; and thethyristor 1748 corresponds to the thyristor 1604. The interconnectmembers 1754, 1756, 1758 and the contact plates 1750, 1752 electricallyinterconnect the varistors 1742, 1744 and the thyristors 1746, 1748 inthe manner represented in FIG. 26.

The subassembly 1740 further includes a coil assembly 1780, anadditional interconnect member 1759, and two additional electricalinsulator layers 1763, 1765. The coil assembly 1780 corresponds to thecoil 1622 of FIG. 26 and is electrically connected to the othercomponents by the interconnect member 1759 in the manner shown in FIG.26.

With reference to FIG. 28, the coil assembly 1780 includes an uppercontact plate 1782, a lower contact plate 1784, a coil member 1786, aninterface member 1787, fasteners 1788, and two coil insulators 1789. Thecomponents 1782, 1784, 1786, 1787 are formed of an electricallyconductive material such as metal (e.g., aluminum).

The coil member 1786 includes a coil body 1786A, a spirally extendingcoil strip 1786B defining a spiral coil channel 1786C, and a couplingextension 1786D. The coil member 1786 is electrically connected to theupper contact plate 1782 via the coupling extension 1786D and to thelower contact plate 1784 via the coil body 1786A. The coil strip 1786Bis electrically insulated from the contact plates 1782, 1784 by theinsulators 1789.

The interconnect member 1759 includes a first contact portion 1759A thatcontacts the lower surface of the lower coil assembly contact plate 1784and the anode of the upper thyristor 1746. The interconnect member 1759also includes a second contact portion 1759B that contacts theinterconnect member 1758 and the anode of the lower thyristor 1748. Theinterconnect member 1759 includes a bridge portion 1759C (not visible inFIG. 27) that electrically connects the contact portions 1759A, 1759B,and thereby the above-mentioned components.

Signal cables 1762A, 1762B corresponding to the signal cables 1062A,1062B extend from the trigger circuit module 1770. Each cable 1762A,1762B includes a gate wire 1762GA, 1762GB and a reference wire 1762RA,1762RB. The gate wires 1762GA, 1762GB are electrically terminated at thecontrol terminals 1745F of the thyristors 1746, 1748 by the gateconnectors 1762D. The reference wires 1762RA and 1762RB are mechanicallyterminated and electrically connected (e.g., by soldering) to the bridgeportions 1757B of the interconnect members 1754 and 1756, respectively.In that way, the reference wire 1762RA is electrically connected to thecathode of the thyristor 1746 through the interconnect member 1754 andthe contact plate 1750, and the reference wire 1762RB is electricallyconnected to the cathode of the thyristor 1748 through the interconnectmember 1756 and the contact plate 1752.

FIG. 29 shows an active energy absorber module 1800 according to furtherembodiments. The module 1800 is constructed in the same manner as themodule 1700, except that the module 1800 does not have an internaltrigger circuit module corresponding to the trigger circuit module 1770and instead employs an external trigger circuit as described above forthe module 1000.

With reference to FIG. 30, an active energy absorber module 1900,according to further embodiments, is shown therein. The module 1900corresponds to the active energy absorber module 201 of FIG. 4. Themodule 1900 is constructed in generally the same manner as the module1700 (FIG. 27), except as follows.

The module 1900 includes an active component subassembly 1940encapsulated in the enclosed chamber 1926 between the housing electrodeend wall 1922A and the electrode head 1927. The subassembly 1940includes a varistor 1942 corresponding to the MOV 206 of FIG. 4,thyristors 1946, 1948 corresponding to the thyristors 202 and 204 ofFIG. 4, an inductor coil 1986 corresponding to the inductance 208 ofFIG. 4, and a trigger circuit module 1970 corresponding to the triggercircuit 210 of FIG. 4.

Interconnect members 1954, 1956 and contact plates 1950, 1952electrically interconnect the varistor 1942, the thyristors 1946, 1948,the coil 1986, and the electrodes 1922A, 1927 in the manner representedin FIG. 4. An electrical insulator 1960 electrically insulates theinterconnect member 1956 from the interconnect member 1954. The triggercircuit of the module 1970 is electrically connected to the gateterminals and cathodes of the thyristors 1946, 1948 by gate wires 1962A,1962GB and reference wires 1962RA, 1962RB via the gate connectors 1962Dand the interconnect members 1954, 1956 in the same manner describedabove for the module 1700 (FIG. 27).

Reference is now made to FIG. 31, which is a schematic block diagramillustrating a device for active overvoltage protection according tosome embodiments of the present invention. An active energy absorber2000 may be connected between power lines 70, 72 in an electricaldistribution system and/or component. The power lines 70, 72 may includepower lines and/or a neutral line in a single phase power system orphase lines and/or a neutral line in a multiple phase system (e.g.,three phase power system). Thus, the active energy absorber 2000 may beconnected between two phase or power lines and/or between a phase orpower line and a neutral line.

Some embodiments provide that an active energy absorber 2000 mayselectively conduct fault current responsive to overvoltage conditions.For example, some embodiments provide that when the active energyabsorber 2000 is in a conducting mode, that the overvoltage conditionmay be clamped to a specific voltage by absorbing energy correspondingto the overvoltage fault condition that exceeds the clamped voltage.Some embodiments are directed to providing protection for temporarypower system sourced overvoltage conditions that may be sustained forlonger periods than transient and/or surge voltages.

In some embodiments, the active energy absorber 2000 includes a triggercircuit 2010 that may be similar to trigger circuit 110 as discussedabove regarding FIG. 3. As such, additional description thereof will beomitted.

The active energy absorber 2000 may include a first thyristor 2002including a first anode, a first cathode and a first gate. The activeenergy absorber 2000 may include a second thyristor 2004 that includes asecond anode that is connected to the first cathode of the firstthyristor 2002, a second cathode that is connected to the first anode ofthe first thyristor 2002, and a second gate. In this regard, the firstthyristor 2002 and the second thyristor 2004 are connected inanti-parallel with one another.

The active energy absorber 2000 may include a first varistor 2006 and asecond varistor 2008. The first varistor 2006 may be connected betweenthe first power line 70 and the second varistor 2008. The secondvaristor 2008 may be connected between the first varistor 2006 and thesecond power line 72. In this regard, the first varistor 2006 and thesecond varistor 2008 may be connected in series with one another.

Some embodiments provide that an inductance 2022 may be optionally usedto reduce the di/dt through the thyristors 2002, 2004 when they conducta surge current. Some embodiments provide that the power lines 70, 72themselves have significant inductance due to their length, the size ofthe cables and any transformer installed upstream to the device.However, inductance 2022 may be connected between the connection node ofthe first and second varistors 2006, 2008 and the connection nodecorresponding to the first cathode of the first thyristor 2002 and thesecond anode of the second thyristor 2004. The first anode of the firstthyristor 2002 and the second cathode of the second thyristor 2004 maybe connected to the terminal of the second varistor 2008 that isconnected of the second power line 72.

In some embodiments, the electrical circuit of the active energyabsorber 2000 may include the SPD functionality. As such, someembodiments provide that the active energy absorber 1600 may be usedwithout an additional and/or external SPD.

Further, during surge events and transient overvoltages, the thyristors2002, 2004 may be self triggered due to their internal parasiticcapacitance between the gate and the anode and the gate and the cathode.According to convention, this parasitic capacitance may be made by themanufacturers to be as low as possible in order to avoid the selftriggering of the thyristors 2002, 2004 in surge events and transientovervoltage events. However, in the current application, the parasiticcapacitance may be higher, which may improve the ease of manufacture. Inthis regard, the device may demonstrate improved sensitivity totriggering during surge events and transient overvoltage events. Assuch, the voltage may not reach very high values before the thryistor2002, 2004 is triggered and the voltage is clamped at the protectionlevel of the varistor 2006, 2008. In this regard, the device mayconsistently clamp at the voltage level of a single varistor 2006, 2008,regardless of whether the event is a temporary overvoltage, a surgecurrent or a transient overvoltage.

The active energy absorber 2000 may not use a snubber circuit as thiscircuit may avoid a false trigger of the thyristor due to high dV/dtduring surge events or transient overvoltages. Instead, the ability ofthe thyristors 2002, 2004 to self trigger may clamp the voltage througha single varistor.

Further, this device may provide stand-alone self-triggered operationthat can be connected in a power system between two lines and provideprotection against temporary overvoltage, transient overvoltage and/orsurge/lightning currents.

With reference to FIG. 32, an active energy absorber module 2100according to further embodiments is shown therein. The module 2100corresponds to the active energy absorber 2000 in FIG. 31. The module2100 is constructed in generally the same manner as the module 1900(FIG. 30) except as follows.

The module 2100 includes an active component subassembly 2140encapsulated in the enclosed chamber 2126 between the housing electrodeend wall 2122A and the electrode head 2127. The subassembly 2140includes a varistor 2142 corresponding to the varistor 2006 of FIG. 31,a second varistor 2144 corresponding to the varistor 2008, a thyristor2146 corresponding to the thyristor 2002, a second thyristor 2148corresponding to the thyristor 2004, an inductor coil 2186 correspondingto the inductance 2022, and a trigger circuit module 2170 correspondingto the trigger circuit 2010.

Interconnect members 2154, 2156, 2158, 2159 and contact plates 2050,2052 electrically interconnect the varistors 2142, 2144, the thyristors2146, 2148, the coil 2186, and the electrodes 2122A, 2127 in the mannerrepresented in FIG. 31. Two electrical insulators 2160 electricallyinsulate the interconnect members 2154 and 2156 from one another and theinterconnect members 2156 and 2158 from one another. The trigger circuitof the trigger circuit module 2170 is electrically connected to the gateterminals and cathodes of the thyristors 2146, 2148 by gate wires2162GA, 2162GB and reference wires 2162RA, 2162RB via the gateconnectors 2162D and the interconnect members 2158, 2159 in the mannerdescribed above for the module 170 (FIG. 27).

Many alterations and modifications may be made by those having ordinaryskill in the art, given the benefit of present disclosure, withoutdeparting from the spirit and scope of the invention. Therefore, it mustbe understood that the illustrated embodiments have been set forth onlyfor the purposes of example, and that it should not be taken as limitingthe invention as defined by the following claims. The following claims,therefore, are to be read to include not only the combination ofelements which are literally set forth but all equivalent elements forperforming substantially the same function in substantially the same wayto obtain substantially the same result. The claims are thus to beunderstood to include what is specifically illustrated and describedabove, what is conceptually equivalent, and also what incorporates theessential idea of the invention.

What is claimed:
 1. A circuit protection device comprising: an activeenergy absorber that is coupled between one of a plurality of phaselines and a neutral line in an electrical power distribution system andthat is configured to selectively conduct fault current responsive toovervoltage conditions; wherein the active energy absorber comprises: asurge protective device that is connected between the one of theplurality of phase lines and the neutral line; an overvoltage protectionmodule that comprises two thyristors that are connected in anti-parallelwith one another; a varistor that is connected with the overvoltageprotection module as a series circuit, wherein series circuit includingthe varistor and the overvoltage protection module is connected betweenthe one of the plurality of phase lines and the neutral line; and aninductor that is connected to the varistor at a junction of the varistorand the one of the plurality of phase lines and that is connected to theurge protective device at a junction of the surge protective device andthe one of the plurality of phase lines.
 2. The device according toclaim 1, wherein the active energy absorber further comprises aninductor that is connected in series with the series circuit includingthe varistor and the overvoltage protection module.
 3. The deviceaccording to claim 1, wherein the varistor comprises a plurality ofvaristors that are connected in parallel with one another.
 4. The deviceaccording to claim 1, further comprising a trigger circuit that isconnected to the one of the plurality of phase lines and the neutralline and to the overvoltage protection module and that is configured toprovide control signals to the overvoltage protection module responsiveto detecting a temporary overvoltage condition across the one of theplurality of phase lines and the neutral line.
 5. The device accordingto claim 4, wherein the trigger circuit comprises: a comparison circuitthat is configured to receive a voltage level signal and a voltagereference signal and to output an overvoltage trigger signal responsiveto the voltage level signal exceeding the voltage reference signal; anda gate trigger circuit that is configured to generate a gate triggersignal responsive to the overvoltage trigger signal that is received bythe overvoltage protection module and that causes the overvoltageprotection module to conduct current corresponding to the temporaryovervoltage condition.
 6. The device according to claim 5, wherein thetrigger circuit further comprises an optical isolation circuit that isconnected between the comparison circuit and the gate trigger circuitand that is configured to provide electrical isolation between thecomparison circuit and the gate trigger circuit.
 7. The device accordingto claim 1, wherein the active energy absorber further comprises asnubber circuit that is connected in parallel with the overvoltageprotection module, wherein the snubber circuit comprises a resistor anda capacitor that are connected in series with one another.
 8. A circuitprotection device comprising: a first thyristor including a first anodethat is connected to a first power line, a first cathode and a firstgate; a first varistor that is connected to the first anode and thefirst cathode; a second thyristor including a second anode that isconnected to a second power line, a second cathode that is connected tothe first cathode and a second gate; a second varistor that is connectedto the second anode, the second cathode, and to the first varistor; anda trigger circuit that is connected to the first and second power linesand to the first gate and the second gate, wherein the trigger circuitis configured to provide control signals to the first thyristor and/orthe second thyristor responsive to detecting a temporary overvoltagecondition across the first and second power lines.
 9. The deviceaccording to claim 8, further comprising an inductor that is connectedto either the first anode or the second anode.
 10. The device accordingto claim 8, wherein the first varistor comprises a plurality of firstvaristors that are connected in parallel with one another, and whereinthe second varistor comprises a plurality of second varistors that areconnected in parallel with one another.
 11. The device according toclaim 8, wherein the first and second power lines comprise any-two oneof a plurality of phase lines and a neutral line.
 12. A circuitprotection device comprising: a first thyristor including a first anodethat is connected to a first power line, a first cathode and a firstgate; a first varistor that is connected to the first anode; a secondthyristor including a second anode that is connected to a second powerline, a second cathode that is connected to the first cathode and asecond gate; a second varistor that is connected to the second anode andto the first varistor; and an inductor that is connected between ajunction of the first and second varistors and a junction of the firstcathode and the second cathode.
 13. The device according to claim 12,further comprising a trigger circuit that is connected to the first andsecond power lines, to the first gate and the second gate, and to thejunction of the first cathode and the second cathode, wherein thetrigger circuit is configured to provide control signals to the firstthyristor and/or the second thyristor responsive to detecting atemporary overvoltage condition across the first and second power lines.